This is a bug from the start of the game. You need to reach Six Paths Sannin at least once for it to fix itself or else you will only ever get ninja school student rewards.

Well, less a bug, more lazy coding. It sloppily explains it at the top of the season rewards page you posted there.

It's a feature!

This is not a bug.

It was intended that to receive the rewards according to your rank, you need to reach Six Paths first at least once. Doing so eliminated the "camp at Super Kage" abuse.

I suppose that makes sense, it's not pointed out very well though and that can still be abused if you get Six Paths at least once, right?

I reached Six Paths once and then i decided to try the "camp at super kage" thing but the game reset me at chunin level. I had 49 pts. Why did this happen?

That explains it. I imagine it resets you every season once you get Six Paths at least once. Though again, like anything translated and done by Oasis, this is either badly explained or not explained at all.